Sputtering is a process based on the disintegration of a cathode material in a vacuum when bombarded by positive ions. Atoms of the cathode material or target are ejected in various directions, and ultimately alight upon and cling firmly to adjacent surfaces, forming a sputtered film. Sputtering is a standard method for producing thin films. This phenomenon can be utilized to form very fine-grained metal coatings on substrates exposed to sputtering. Glass plates may thus be silvered, or suspension fibers of spun quartz rendered conductive for use in electrometers, etc. In addition to metal films, sputtering can be used to deposit films of a broad range of insulators and semiconductors on various substrates. Films composed of more than one material can be obtained by using cathodes or targets made of those materials. Normal sputtering operations for film deposition employ sputtering gas pressures of 0.01 Torr or less.
Various sputtering related techniques are known for producing composite materials. Rairden, U.S. Pat. No. 3,655,544 discloses a sputtering method, performed at a constant pressure within the range of 1.0 to 200 milliTorr, for producing a resistor film, consisting essentially of tungsten, molybdenum and their respective nitrides, on an alumina substrate, wherein electrical contact can then be made to the resistor film by depositing aluminum on the film by vacuum evaporation at pressures less than 5.times.10.sup.-5 Torr. Miyake et al., U.S. Pat. No. 4,349,425 discloses a sputtering method, performed at a constant pressure within the range of 10.sup.-3 to 10.sup.-1 Torr, which utilizes a mixture of inert gas and oxygen gas for oxidizing sputtered metal atoms to form a film of the oxides of cadmium and tin. Pirich et al., U.S. Pat. No. 4,484,995 discloses a sputtering method, performed at a constant pressure within the range of 10 to 200 milliTorr, for producing a coating of a ferromagnetic alloy of a rare earth-transition element mixture on an aluminum substrate at substrate temperatures as low as 25.degree. C. Hitosuyanagi et al., U.S. Pat. No. 4,496,450 discloses a process, performed at a constant pressure within the range of 5.times.10.sup.-3 to 1 Torr, for producing a multi-component thin film which includes joint use of a sputtering method and a plasma chemical vapor deposition (CVD) method which produces an amorphous silicon material having a sputtered aluminum dopant. None of the aforementioned processes will produce a phase separated composite comprising a continuous phase matrix of a first element having discrete nanoscale particles of a second element dispersed therein.
Phase-separated materials have been used in electronic, magnetic, and glass-ceramic applications. It is possible to deposit certain limited classes of phase-separated composite thin films by ordinary thin film deposition techniques, but only if the two components are immiscible and do not form stable compounds. For example, composites of iron particles in a matrix of amorphous silica can be produced by cosputtering iron and silica [See Holtz et al., "Enhanced Magnetic Anisotropy at the Percolation Threshold of Fe-SiO.sub.2 Composite Thin Films", Appl. Phys. Lett., Vol 56, No. 10, pp. 943-5 (1990)]. The possible applications of phase-separated materials are limited, however, by the fact that immiscible materials must be used in order to avoid the formation of alloys, and materials which do not react with each other must be used, in order to avoid the formation of new chemical compounds. This greatly restricts the choice of materials which can be used.